Experiments are in progress to elucidate three aspects of SV40 DNA replication in primary African Green Monkey Kidney Cells: 1) initiation of DNA replication, 2) polynucleotide chain propagation, 3) segregation of newly synthesized progeny DNA molecules. The effects of viral mutants, cell line varients and inhibitors of DNA synthesis and protein synthesis on these three processes of replication are being studied. In vitro DNA replication systems are presently being optimized to detect proteins required for each of these three steps in replication. The use of E. coli and T-4 replicative enzymes and proteins to substitute for the mammalian functions is under investigation.